There
are two parameters that govern the characteristics of the atmosphere:
the solar flux and the geomagnetic index. These two parameters will
determine as accurately as possible the atmospheric density at orbital
altitudes based on solar activity. The density is then incorporated
into the state vector propagation process in its atmospheric drag
computations.

NASA SkyWatch uses its internal
table of appropriate values that are future predicted based on the
11-year solar cycle. Alternatively, the user can input the values
based on another source. During shuttle flights, the Flight Dynamics
Officers will provide state vectors for the shuttle and also the current
values of solar flux and geomagnetic index. The Atmospheric Defaults button
resets the internal atmospheric values.